Elevator units comprise an elevator car which is movable in an elevator shaft. It is common to install buffers as safety devices in a pit of the elevator shaft, in order to decelerate the elevator car as it travels past the lowest stop (or the counterweight as it travels past the topmost stop) in the event of malfunction of the drive. In elevators with high nominal speeds, very large buffers are required for this purpose. Large buffers require a deep pit, which is expensive to construct. Use of buffers satisfies safety regulations which prescribe that the elevator unit must be designed and constructed so as to prevent the car from crashing in the elevator pit (see, e.g., European Safety Standard EN81).
In order to be able to make the buffers and hence the pit smaller, deceleration control circuits have already been proposed which allow the use of smaller single-use buffer devices as described for example in DE 20104389 U1 and DE 1021063 A1.
An excess speed detector with a plurality of light barriers arranged on the elevator car is already known from EP 0712804 B1. The light barriers generate measurements using a measuring strip attached to one side of the elevator shaft, and the speed or deceleration of the elevator car can be determined using these measurements. The measuring strip is of a redundant construction and consists of a marking track and a control track.
Moreover, in addition to the braking device provided for the elevator car, it is conventional and known to provide a catching device for emergencies, and this catching device comprises, in particular, catching wedges (cf. DE 29912544 U1).